Vinyl ethers containing fluorine and also chlorine are of particular interest in coatings applications because they form polymers and copolymers that exhibit beneficial properties, including high chemical and thermal resistance, high electrical resistivity, low surface energy and low refractive index. These properties can be imparted to a coating surface and, consequently, halogenated vinyl ethers are particularly useful in making protective coatings, release coatings, as well as, surfactants, anticorrosion agents, antioxidizing agents and the like.
Some fluorinated chemical compounds are known in the art which contain oxyvinyl groups such as are described in U.S. Pat. No. 2,732,370 under the generic formula C.sub.n F.sub.2n+1 CH.sub.2 --O--CH.dbd.CH.sub.2. The fluorinated structures near the oxyvinyl group are believed either not to be radiation curable or not to have radiation curable reactivities to the extent desired.
JP 2,000,721 discloses aliphatic fluorinated vinyl ether compounds having the structure R'R"CH--O--CH.sub.2 CH.sub.2 --O--CH.dbd.CH.sub.2 wherein R' is a hydrogen, a lower alkyl group or a polyfluoroalkyl group and R" is a polyfluoroalkyl group. U.S. Pat. No. 5,012,011 discloses the synthesis of fluorinated vinyl ethers such as CF.sub.3 (CF.sub.2).sub.x R.sub.1 OCH.sub.2 CH(OH)R.sub.2 OCH.dbd.CH.sub.2 (R.sub.1.dbd.C1-C20 alkylene, alkoxyethylene, arylene, aryloxyalkylene; R.sub.2.dbd.C1-C100 divalent organic radicals; and x=1-22). Fluorinated vinyl compounds containing a hydroxyl or alkoxy group are described by U.S. Pat. No. 4,559,179. The preparation of H(CF.sub.2 CF.sub.2).sub.n CH.sub.2 OCH.dbd.CH.sub.2 (n=2-4) is reported by Sukhinin et al., Zh. Vses. khim. O-va., 26(3), 344-5 (1981). Because of the heavily fluorinated structure, adherence to substrates and compatibility with solvents and cosolutes may not be as good as desired.
Moreover, vinyl ether monomers or copolymers that can be cured via ultraviolet (UV) radiation offer even more advantages in coatings and other applications. Photocuring technology has grown rapidly within the last decade. The photocuring process involves the radiation induced polymerization or cross linking of monomers into a three dimensional network and has a number of advantages including the environmentally safe, solvent-free 100% conversion to a desired product, as well as short cycle times and limited space and capital equipment requirements.
In the telecommunications industry, for example, there is a need to develop photocurable compositions for optical wave guide and interconnect applications. In order to be useful in these applications, the photocurable compositions must polymerize to form polymers that are highly transparent at the working wavelength and possess low intrinsic absorption and scattering loss.
U.S. Pat. No. 5,274,174 discloses a new class of photocurable compositions comprised of certain fluorinated monomers, such as diacrylates with perfluoro or perfluoropolyether chains, which possess low intrinsic absorption loss. It is, therefore, possible to make low loss optical interconnects from a photocurable system including these materials.
Fluorine substitution in the polymer structure, however, also induces some other less desirable changes in the polymer's physical properties. One such change is the decrease in refractive index. For a highly fluorinated acrylate photopolymer, the refractive index decreases to the 1.32 region when the H/F mole ratio reaches 0.25. For optical interconnect applications, to avoid loss of light, it is important that the refractive index of the core of a planar waveguide approximate and preferably match that of the optical fiber (generally 1.45).
It is also important to be able to precisely control and fine tune the refractive index of the photopolymer at the working wavelength in optical waveguide and interconnect applications. A desired index of refraction can be produced by mixing photocurable monomers with different refractive indices. Most photopolymers made from conventional photocurable monomers have refractive indices in the region of 1.45-1.55. Depending on the application, it is often desirable to lower a photopolymer's refractive index. One way to do this is to mix low refractive index fluorinated monomers with conventional hydrocarbon-based monomers. Unfortunately, this is difficult to accomplish because of the incompatibility or insolubility of the different monomer systems. Thus, there is a need for photocurable compositions which: (i) possess low intrinsic absorption loss in the near-infrared region; (ii) possess a refractive index approaching traditional optical fibers; and (iii) are compatible with both conventional hydrocarbon-based and highly fluorinated monomers.